The present invention relates to a hydraulic lifter or clearance adjuster for use in a valve operating mechanism of an internal combustion engine.
A hydraulic lifter takes up all clearance in the valve train all the time during engine operation, and absorbs thermal expansion of the valve stem or other members by changing the length of the lifter itself. If, however, air is contained in hydraulic fluid and introduced into the hydraulic lifter together with the hydraulic fluid, the hydraulic lifter cannot correctly perform its function and cannot maintain quiet operation any more. Besides, a plunger of the hydraulic lifter must be held not only easily slidable axially but also it must be easily rotatable on its own axis in order to prevent uneven wear of contacting parts.